Most likely brake fluid, like frango said, check the brake lines and caliper for the source of the leak.

However, if it is a heavy oil with a rotten egg smell to it then its gear oil leaking out of the end of the axle shaft seal. Had this happen on my old ZJ, was all ready to replace the brakes and after taking the wheel and drum off I found the real source of the leak.

poke your head under the car (from the rear)... look at the brake backing plates. If either one is coated, that is your problem. The axle seals are decently common on the wj.

Also very well could be brake fluid, but if your leaving trace of it, its not going to be a small leak and you would already be feeling poor braking due to lack of fluid. Also if you were not out of brake fluid in that circuit you would feel a sinking pedal when you applied the brakes.

btw, i have regularly heard the diff lube and lsd additive refered to as having a "rotten egg" smell. Personally I dont think it does, its not a great smell but hardly rotten egg.

viscosity will be a big factor if its thick and slimy and takes soap or clothes to wipe it on to get it off your fingers its diff lube, if it will wash off with water and its thin and watery between your fingers (rubbing thumb and index together), its going to be brake fluid.

Again, it VERY well could be brake fluid, but especially by now almost a week later if your leaving drips on the ground your master cylinder has got to be low or empty by now. pop your hood and check the level. If your low (like below min) its likely brake fluid.

edit: on odds alone I would lean towards axle seal as the link posted with their jeep with 100k or less the seals were alread dumping. Axle seals on a wj are VERY common, leaking brake fluid from a caliper... not so much... BUT possible none the less.

Yeah $500 was a little steep for both rear seals plus differential seal and refill. Pays to know someone for sure! Usually I do everything myself but this seemed like a harder job then I thought with the axle having to be released from the differential to replace the seals

I just had the same issue with mine. 2001 wj with 85,000 miles. I had them replace both rear axle seals it cost me around $500

Scott

Did you have the job done at the stealer? I had mine done at a local shop and they replaced the brake pads, turned the rotors and left the parking brake shoes as they were after cleaning them with brake cleaner. Total price was $440.